1. Field of the Invention
This invention relates to an improved method and apparatus for controlling the cooling and heating capacity of a variable speed heat pump using non-azeotropic refrigerant mixtures to maintain an optimum match between the heat pump capacity and the load requirement of a conditioned space.
2. Description of the Prior Art
The application of mixed refrigerant systems to heat pumps, air conditioning systems, chillers, and refrigerators/freezers represents known prior art. Such an application is disclosed by U.S. Pat. No. 4,722,195 which teaches a heat pump apparatus using a non-azeotropic refrigerant mixture in which the refrigerant mixture is circulated in a main refrigeration circuit and the high pressure and low pressure refrigerant components of the mixture are separated by a rectifier. The higher pressure refrigerant is stored in a reservoir to permit a mixture having a higher content of lower pressure refrigerant to recirculate in the main refrigeration circuit during a low power mode of operation. The higher pressure refrigerant is released from the reservoir to permit a mixture with an intrinsic ratio of higher-to-lower pressure refrigerants to recirculate in the circuit during high power mode operations. The rectifier circuit for separating the higher pressure refrigerant from the lower pressure refrigerant includes a rectifier, a reservoir for storing separated higher pressure refrigerant in liquid phase and feeding an overflowed portion of the stored refrigerant back to the rectifier, a condenser disposed between the top of the rectifier and the reservoir to condense vaporized fluid, a capillary tube in communication with the bottom of the rectifier, and a solenoid valve in communication with the bottom of the reservoir, and at the other end of the capillary tube serving as a by-pass to the rectifier circuit. Two check valves are employed in conjunction with the capillary tubes to control the flow of working fluid into the main refrigeration circuit.
Other such applications are disclosed by U.S. Pat. No. 2,841,965 which teaches a multi-refrigerant, dual capacity refrigeration system in which a three-way valve in combination with a load sensing device is used to control the refrigerant composition; U.S. Pat. No. 2,492,725 which teaches a multi-refrigerant system in which refrigerant vapor and refrigerant liquid flow together in a parallel relationship such that in condensing the refrigerant mixture, initial condensation, which occurs at a relatively high temperature, results in formation of condensation rich in the component of higher boiling point and poor in the component of the lower boiling point; U.S. Pat. No. 2,867,094 which teaches a multi-refrigerant system in which a threeway, three-position valve is used in conjunction with a load sensing and sequence control device to control the composition of the refrigerant; U.S. Pat. No. 2,938,362 which teaches a multi-refrigerant system having a compressor of fixed biometric displacement, a condenser, an evaporator, and an expansion valve or capillary tube between the condenser and evaporator to reduce the pressure of the refrigerant flowing from the condenser to the evaporator, which components make up an active refrigeration circuit, and a rectifier in a refrigerant rectifier circuit, having a heater in the base to heat the refrigerant mixture and activate the system; U.S. Pat. No. 4,423,603 which teaches a heat pump refrigeration system for air conditioning utilizing multiple refrigerants in which the suction side and discharge side of a compressor are switchable between an indoor heat exchanger and an outdoor heat exchanger by a four-way valve for controlling the relative concentrations of the refrigerants; and U.S. Pat. No. 4,769,999 which teaches a gas-liquid contactor for use in a refrigeration cycle for varying the mixing ratio of a non-azeotropic refrigerant mixture circulated through the refrigeration cycle.
Multi-refrigerant systems for refrigerators are disclosed by U.S. Pat. Nos. 4,416,119 and 4,439,996 while U.S. Pat. No. 2,951,350 teaches an absorption refrigeration system in which molecular sieve is used an absorbent. U.S. Pat. No. 4,671,077 teaches an ice maker heat pump which uses water supercooling.
U.S. Pat. No. 4,528,823 teaches a heat pump apparatus having a main refrigerant circuit and an auxiliary shunting refrigerant line having a compressor, condenser, and a pressure reducer means for shunting from the gaseous phase portion of the gas-liquid separator of the main refrigerant circuit and merging in the evaporator of the main refrigerant circuit.
Other applications of non-azeotropic refrigerant mixtures to heating and cooling processes are disclosed by U.S. Pat. Nos. 4,724,679, 4,843,837, and 4,961,323. U.S. Pat. No. 4,777,805 discloses a multi-stage heat pump system using a single working medium in which the condenser or evaporator has a plurality of heat exchange chambers, and the compressor has a plurality of ports (suction or delivery) that are on different pressure levels.
Various azeotrope-like mixtures are disclosed by U.S. Pat. Nos. 4,943,388, 4,948,526, 4,978,467, and 4,997,589.